Sequence a: 4, 8, 12, 16, 20, ...
As you can observe, this is an arithmetic sequence with a difference of 4 because each new term is 4 units more than the previous one: 4+4=8, 8+4=12, 12+4=16,...
We have to use the function for arithmetic sequences

Where f(1) = 4 and d = 4. So, the function is

Hence, the function of the sequence a is f(n) = 4n.
Sequence b: 1, 4, 16, 64, 256, ...
This sequence is geometric because each new term is four times its previous one: 1x4=4, 4x4=16, 16x4=64,...
We have to use the function for geometric sequences

Where f(1) = 1 and r = 4.

Hence, the function is

Sequence c.
As you can observe, this sequence is formed by the same number, which means it represents a constant function like the following
![f(n)=\sqrt[]{3}](https://img.qammunity.org/2023/formulas/mathematics/college/z5mnegunpmbyzi8v7szhbw25mw8vc9b4wy.png)